One of the first glutamate uncaging (p-hydroxyphenacyl-glutamate) experiments on dendrites was done by Kandler (1998) on CA1 pyramidal neurons in slices . They reported the long-term depression of glutamate responses after the pairing of uncaging with depolarization of the neuron. A similar result was obtained with bursts of uncaging by Dodt (1999); these authors used an infrared-guided laser stimulation system to uncage glutamate on the apical dendrites of layer 5 neocortical pyramidal neurons.
The traditional uncaging groups, such as nitrobenzyls, are designed for one-photon uncaging.
Newer caged glutamate compounds have been designed for 2-photon uncaging. Furuta (1999) designed a bromo-hydroxycoumarin-caged compound (Bhc-glutamate) that is more than an order of magnitude more sensitive than carboxynitrobenzyl-glutamate (CNB-glutamate). The synthesis of Bhc-glutamate allowed the creation of three-dimensional maps of the glutamate sensitivity of pyramidal neurons in brain slices.
- caged-glutamate compound
- based on ruthenium photochemistry
- excited with visible wavelengths
- releases glutamate after 1-photon or 2-photon excitation.
- high quantum efficiency
- can be used at low concentrations,
- partly avoids blockade of GABAergic transmission
- 2-photon uncaging of RuBi-Glutamate has a high spatial resolution and generates excitatory responses in individual dendritic spines with physiological kinetics.
- With laser beam multiplexing, two-photon RuBi-Glutamate uncaging can also be used to depolarize and fire pyramidal neurons with single-cell resolution.
- RuBi-Glutamate enables the photoactivation of neuronal dendrites and circuits with visible or two-photon light sources, achieving single cell, or even single spine, precision.
ruthenium-bipyridine complexes can be used as caging compounds. ruthenium is a transition metal with versatile chemistry. polypyridines of ruthenium photorelease entire ligands in a heterolytic fashion, by means of a widely known mechanism in which the initial photoexcited state quickly evolves into a dissociative state, so the photorelease is therefore clean and fast.
- Pros: RuBi-Glutamate
- minimal antagonistic effects on GABAergic transmission
- Cons: RuBi-Glutamate
- not much prior literature to demo the effects
- Pros: MNI-glutamate
- lots of prior literature to demo the effects
- antagonist of GABAergic transmission at high concentrations
- Cons: MNI-glutamate
- needs to be applied to the tissue at relatively high (mM) concentrations for effective 2-photon uncaging.
- antagonist to GABAergic transmission so can't be used to study GABAergic neurons
L-glutamic acid α(4,5-dimethoxy-2-nitrobenzyl) ester (Callaway, Katz, 1993)
- Kandler, Katz, Kauer 1998 Focal photolysis of caged glutamate produces long-term depression of hippocampal glutamate receptors
- Araya Yuste 2006 The spine neck filters membrane potentials
- Carter Sabatini 2004 State-dependent calcium signaling in dendritic spines of striatal medium spiny neurons
- Gasparini Magee 2006 State dependent dendritic computation in hippocampal CA1 pyramidal neurons
- Matsuzaki Kasai 2001 Dendritic spine geometry is critical for AMPA receptor expression in hippocampal CA1 pyramidal neurons
- Sobczyk Svoboda 2005 NMDA receptor subunitdependent Ca2 signaling in individual hippocampal dendritic spines
- Callaway Yuste 2002 Stimulating neurons with light